Saturday, 27 October 2012

Were Humans Responsible for the Extinction of Megafauna in Australia?

We have already seen in the previous blog that humans played a huge part in the extinction of megafauna during the Pleistocene. Whilst there is much controversy as to the cause of megafaunal collapse during this period, this blog will review whether man can be solely blamed for the extinction of over 60 faunal species in Australia. Extinctions mainly occured with terrestrial megafauna, leaving marine megafauna untouched (Stuart 1999). Consequently, the Australian megafauna that became extinct 46.4 kyr mostly comprised of large marsupials, birds and reptiles. Humans evolved in Africa, but it is believed that over 85,000 years ago humans left this continent and traveled through the Southern Arabian peninsula towards India. From here, they expanded in all directions with some crossing from Timor into Australia around 65,000 years ago. As a result, there is much debate as to suggest whether the timing of first human colonization and the extinction of mega fauna is a coincidence (Field 2008), or whether man was the cause. Johnson (2006) believes that most if not all of the 68 mega faunal species became extinct at the time of human arrival on the Australian continent, subsequently disappearing within 5000 years. Evidence for the over kill hypothesis is found in the remains of butchered megafauna in Cuddie Springs in New South Wales. Animal remains at the springs dated well after previously though date of extinction, suggesting that protracted overkill was the likely explanation. 
Genyornis Newtoni

Australia suffered the greatest number of losses including 14 of 16 Pleistocene mammalian genera, 6 reptiles and at least 3 birds, including the flightless bird Genyornis newtoni  (Murray, 1984, 1991; Koch andBarnosky, 2006).  Difficulty in finding the reasons behind such losses are due to the fact people routinely dismember and butcher animals in the process of consumption, and as a consequence of this behavior  remains are rarely if ever found (Field et al 2008). Evidence that supports the claim that humans were responsible for mass faunal extinction is found in the demise of animals that were resilient to glacial interglacial cycling. Recently, the identification of some faunal species having adaptations to aridity has been forwarded as evidence that climate change was not a major force driving this process. By default, humans must have been responsible (Field et al 2012). Further evidence includes the disappearance of G.newtoni in central Australia, which coincides with initial human colonization in the region. Man could have caused this disappearance due to hunting practices over long periods, or possibly through habitat fragmentation which would have altered the landscape causing large scale extinctions. Evidence of landscape modification is shown in the increase of charcoal found in fossil records. A study of Tight Eastern Cave in South West Australia showed that charcoal concentration rose immediately after human arrival. This indicates that human induced habitat modification might have caused the extinction of megafauna and not over kill.  However whilst the increase of charcoal is evident, fire frequency during the Holocene from c8.5kyr does not bare any relationship to human activities (Field et al 2008). High loss of large browsing herbivores (above 30kg) over smaller grazing herbivores, also reinforces evidence to suggest that over hunting is a likely cause of high extinction rates. Similarly, the fact that there is very little evidence of coexistence between humans and megafauna implies man being responsible for such losses. The suggestion that climate could have been responsible for the decline of mega fauna is undermined by the fact that climate change in this region was relatively ‘mild’. 

Overall, reasons for the extinction of mega fauna in Australia are complex. Whilst there is evidence to suggest that the colonization of humans in the region was the primary cause of faunal extinction, there is still lack of supporting evidence. Australia is such a dry continent and ‘stratified sequences are few and far between’ (Field et al 2012). Consequently lack of fossil evidence and poor data sets are fundamental obstacles facing scientists trying to resolve this extinction controversy. Whilst there is strong evidence to suggest hunting and habitat fragmentation is a likely cause of extinctions, there is still much debate as to whether such practices were a result of changing climatic conditions. In later blogs I will discuss how the extinction process is even more complex, suggesting other possible factors explaining the decline of mega fauna in the late Pleistocene.

When our early ancestors entered new lands they encountered a variety of strange new creatures..... Enjoy! 

Johnson, C.N., 2006. Australia's Mammal Extinctions: A 50 000 Year History. Cambridge University Press, Melbourne.

Thursday, 18 October 2012

Is Human Overkill Responsible for Megafauna Extinction?

There is much controversy as to the cause of megafauna collapse in the late Pleistocene. Whilst there is much evidence to support the influence of climate and disease, I will discuss the importance of human overkill in driving widespread extinction.

About 12,000 years ago one of the great scientific mysteries occurred. Up until that time, during the first 2 million years of the Pleistocene, species rarely went extinct (Bulte et al 2006). But then, around 12,000 years ago megafauna such as Deinotherium and mammoths disappeared. Evidence of this disappearance is stated by Bulte et al (2006) who states that the Americas lost 57 large mammals, including three genera of elephants, an average of one every thirty years. Many believe that overkill was responsible for such extinction, with hunters preying on large mammals leading to their demise. Growing support for the overkill hypothesis is due to extinction events in North America and Eurasia coinciding with the arrival of Homo Sapians. Similarly, evidence to support the overkill hypothesis is mentioned by Roberts et al (2001) who found that extinction in Australia did not coincide with extreme climatic events. It is important to note two theories within the overkill hypothesis. Blitzkrieg theory suggests that hunting occurred over intense periods, whilst Protracted Overkill states that extinction (from hunting) happened over longer timescales. Another factor which corroborates the over kill hypothesis is findings of advanced tools/weapons such as spears, harpoons and nets. Such tools provide evidence that Homo Sapiens had the ability to cause the extinction of megafauna. In contrast, some reject this hypothesis, stating that sophisticated technology might have caused primitive man to vary his diet, eating other forms of food such as fish and shellfish (Hoffecker 2005), and thus reduced hunting of megafauna.

Poor quality fossil data sets make it exceptionally hard to discover whether it was climate or primitive man that caused mega fauna collapse. Similarly, the lack of found 'kill sites' weakens this theory. Alternative hypotheses questions whether humans had access to an alternative food source (most likely from agriculture). Had man not obtained another food source wouldn't the extinction of megafauna would have caused humans to die out? Furthermore, if a substitute food source was available, this would have required a large amount of time and labor to sustain, thus limiting hunting time. Others reject this hypothesis as they believe the advancement of agriculture would have caused human populations to grow faster, which in turn may have increased hunting. Bulte et al(2006) proposes an alternative theory in which the rapid hunting of “mini-fauna” e.g. deer and hares would have increased chance encounters with mega fauna, leading to their eventual extinction. Humans can also cause extinction through habitat alteration (through the use of fire), introducing non-native species which act as predators on megafauna and by spreading pathogens (Barnowsky et al 2011)

Therefore, evidence suggests man had a huge impact on mega fauna during the late Pleistocene. Whether such influence was enough to cause the extinction of mega fauna is still unknown. Whist evidence from palaeontology, climatology archaeology, and ecology now supports the idea that humans contributed to extinction on some continents, human hunting was not solely responsible for extinction everywhere (Barnosky et al 2004). In my next blogs I will explore alternative hypothesis such as the role of climate, disease, and the possible impact of an extra-terrestrial event (12,900 years ago), which are all plausible explanations for the extinction of mega fauna during the Pleistocene.

An insight into the life of a hunter gatherer during the Pleistocene era:

The hunt is on: famous 10,000 BC clip of a mammoth hunt: Enjoy!

Friday, 12 October 2012

The Journey Begins

This is my first ever blogging assignment, and I would like to take this opportunity to look at the various factors that could have caused the collapse of megafauna during the late Pleistocene (60,000-11,000 years ago). This topic is particularly fascinating as I have always wanted to understand whether man, climate or another factor  was responsible for the death and eventual extinction of these great beasts. My curiosity was first sparked when I watched 10,000 BC (many of you have probably seen it), whereby I was intrigued as to whether the colonial expansion of Homo Sapiens could cause the complete extinction of such large animals.  Even well-loved children animated films such as Ice-Age arouse much debate around this topic. Megafauna can be defined by archaeologists and palaeontologists as 'large bodied mammals weighing more than 100 pounds'.  Many of the megafauna that died between 40,000 and 10,000 years ago (Pleistocene mega fauna) weighed approximately 4,500kg, that’s three times heavier than your average car!!
My blogs will specifically question whether it was a coincidence that megafauna became extinct just as humans left Africa and Southern Asia and began to colonize the rest of the world.  I will also address  other hypothesis that have been given for these extinctions, including climatic change, disease, fire and the impact from an asteroid/comet.
Eurasia: wooly mammoth
Australia: Diprotodon (giant wombat)
South America: Smilodon (Sabertooth)
I will also discuss whether its possible that these forces worked together, subsequently causing extinctions. As this journey of discovery progresses, we will uncover various reasons for the extinction of megafauna in the continents of Australia, Asia and Africa. Evidence has shown that when the planet became colder some animals did not adapt quickly enough and consequently died out.  Changes in climate could have induced human migration or the spread of disease.
With the use of dating, modelling, and genetic analysis there has been a large degree of research conducted as to the reasons behind megafauna extinction. However, the conclusions of of these studies have been controversial. By the end of this blog, I  hope to shed some light on one of the greatest mysteries that to this day, has no accepted answer. 

The youtube video below provides a brief background as to what I will be discussing in my later blogs.